The healthy heart produces regular, synchronized contractions. Rhythmic contractions of the heart are normally controlled by the sinoatrial (SA) node, which is a group of specialized cells located in the upper right atrium. The SA node is the normal pacemaker of the heart, typically initiating 60-100 heartbeats per minute. When the SA node is pacing the heart normally, the heart is said to be in normal sinus rhythm.
If the heart's electrical activity becomes uncoordinated or irregular, the heart is denoted to be arrhythmic. Cardiac arrhythmia impairs cardiac efficiency and may be a potential life-threatening event. Cardiac arrhythmias have a number of etiological sources, including tissue damage due to myocardial infarction, infection, or degradation of the heart's ability to generate or synchronize the electrical impulses that coordinate contractions.
Bradycardia occurs when the heart rhythm is too slow. This condition may be caused, for example, by impaired function of the SA node, denoted sick sinus syndrome, or by delayed propagation or blockage of the electrical impulse between the atria and ventricles. Bradycardia produces a heart rate that is too slow to maintain adequate circulation.
When the heart rate is too rapid, the condition is denoted tachyarrythmia. Tachyarrythmia may have its origin in either the atria or the ventricles. Tachyarrythmias occurring in the atria of the heart, for example, include atrial fibrillation and atrial flutter. Both conditions are characterized by rapid contractions of the atria. Besides being hemodynamically inefficient, the rapid contractions of the atria may also adversely affect the ventricular rate.
Ventricular tachyarrythmia occurs, for example, when electrical activity arises in the ventricular myocardium at a rate more rapid than the normal sinus rhythm. Ventricular tachyarrythmia includes ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia may quickly degenerate into ventricular fibrillation. Ventricular fibrillation is a condition denoted by extremely rapid, uncoordinated electrical activity within the ventricular tissue. The rapid and erratic excitation of the ventricular tissue prevents synchronized contractions and impairs the heart's ability to effectively pump blood to the body, which is a fatal condition unless the heart is returned to sinus rhythm within a few minutes.
Implantable cardiac rhythm management systems have been used as an effective treatment for patients with serious arrhythmias. These systems typically include one or more leads and circuitry to sense signals from one or more interior and/or exterior surfaces of the heart. Such systems also include circuitry for generating electrical pulses that are applied to cardiac tissue at one or more interior and/or exterior surfaces of the heart. For example, leads extending into the patient's heart are connected to electrodes that contact the myocardium for sensing the heart's electrical signals and for delivering pulses to the heart in accordance with various therapies for treating arrhythmias.
In late 1980s, studies identified groups of patients that could benefit from the use of implantable cardiac defibrillators (ICDs). Implantation of ICDs became the medical standard of care for those patients determined to have the indicated level of health risks.
Over time, post market studies have identified a large group of patients who would meet the determined risk levels, but will not receive benefits from these devices in the immediate years. Therefore, such patients would receive an ICD and the device would stay in the body for a long time without ever firing or shocking the patient's heart. The current devices are designed to address complex arrhythmias and implantation of them in the initial group of patients is deemed as unnecessary, and economically irresponsible. Thousands of patients are given devices that treat more than they are at risk for, as the current devices on the market are developed to treat and handle a multitude of cardiac conditions. Additionally, the devices require a specialist to implant and often need a programmer or consultant to initially program the device.
ICDs are utilized more frequently as prophylactic devices for treatment of sudden cardiac death (SCD). In addition to implantable devices, automated external defibrillators (AEDs) are also effective in treatment of SCD but require administration of the therapy by an outside agent (such as a bystander). As long as the AED treatment is given to the patient within the first 2-3 minutes from the onset of the event, the patient will likely have a positive response to the treatment. Studies have shown that more than 75% of the SCDs occur at home and over half occur in the bedroom. Patients at risk of SCD are often alone and asleep and would need their safety product nearby and not rely on the help of a third party.